I frequently "sir" and "ma'am" people. I work in public service in a state that has both strong northern and southern roots, depending on which county you're in. It's become a habit, and it's meant with nothing but the utmost respect. The "northerners" don't seem to mind it, the "southerners" seem to like it, and it's more polite IMO than "hey you" when I don't know someone's name.

That said, I really dislike being called "Miss Becky", although I tolerate it if it's children who are doing so. I had a boss call me "Miss Becky" once in an office-wide meeting, and I didn't like it. I guess that occurence has left a bad taste in my mouth for the expression.